They can be a tough, it's usually dirt and dry o'rings. Try using some lube then attach the tool...pull hard or shock it with something soft like a plastic handled screwdriver (hide the BFH) haha
I have a tool with all the sizes and the only one that will fit in the opening is the 5/8", plus I have a set of the plastic ones and the 5/8" is the only one of them that will fit inside the spring connector. I do have an air compressor I will try blowing it out good either tomorrow or Monday. Keep the ideas coming. Tapping the fitting didn't do any good as far as loosening it up. I don't understand why they didn't just use a threaded fitting like they use on the compressor. I guess they figure that's too damn simple and that any idiot can figure it out. The bad thing is if I get this one repaired, when I go to visit my parents I need to repair a leak on my dad's '94 Escort. Dad's 81 years old and mom is 78 so they need their a/c working during the hot summer months. I sure hope their problem is something besides one of the spring lock connectors.If you can twist it then the spring is not released yet. There are several different size tools for that job. Make sure you are using the right one. If you have access to compressesd air blow all around the fitting inside where the spring is. All it takes is a small amount of dirt to stop the tool from moving the spring back. Some of those fittings require real determination.